[62.04] Sizing Up Close-In Planets Around Sun-Like Stars

D. Charbonneau (Harvard-Smithsonian CfA & HAO/NCAR)

Radial velocity surveys of nearby F, G, K, and M dwarf stars
have revealed a class of close-in massive planets that orbit
their stars with a separation of less than 0.1 AU. Close-in
planets such as these will produce a measurable photometric
dimming of the star if the planet transits the stellar disk.
The search to measure the transit photometrically is
motivated by the fact that, for a star for which both the
radial velocity and transits are observed, one can estimate
both the mass and radius of the planet. These can then be
combined to calculate such critically interesting quantities
as the surface gravity and average density of the planet,
and thus provide the first constraints on structural models
for these low-mass companions. I will discuss the STARE
project (a small-aperture, wide-field telescope that
monitors thousands of stars for planetary transits), which
we used in September 1999 to detect the first planetary
transits across a Sun-like star. I will focus on two of the
follow-up measurements that we have undertaken for this
system: First, exceptionally high-precision, rapid-cadence
photometric monitoring with HST/STIS allows us to search for
Earth-sized planetary satellites, and circumplanetary rings.
Second, high-resolution, high-precision spectroscopy during
transit may reveal additional features due to absorption by
the planetary atmosphere.

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